In order to prepare neutrophils and macrophages, the changes in number and composition of peritoneal exudate cells (PEC) of yellowtail after injection of Pasteurella piscicida formalin killed bacteria (FKB) or proteose-peptone, respectively, were studied. The increases of PEC after injection of P. piscicida FKB was greater than that after injection of proteose-peptone. Most of the cells in the peritoneal cavity of healthy fish were lymphocytes. After injection of any of the two substances, neutrophils, eosinophils and basophils appeared at firstly, and followed by macrophages. The percentage of the lymphocytes gradually decreased. However, the appearance of macrophages in the group injected with P. piscicida FKB was earlier than in the group injected with proteose-peptone. The peak of neutrophils in PEC was observed at 6h after injection of P. piscicida FKB and 12h after injection of proteose-peptone. The peak of macrophages in PEC was observed at 48h after injection of P. piscicida FKB and 192h after injection of proteose-peptone.According to the data, P. piscicida FKB shows in elicite the exudation of macrophages into peritoneal cavity than proteose-peptone.
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